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BEGIN:VEVENT
DTSTART;TZID=Atlantic/Canary:20220524T170000
DTEND;TZID=Atlantic/Canary:20220524T180000
UID:iactalks-1590
X-WR-CALNAME: IAC Talks: Open Astronomy Seminars
X-ORIGINAL-URL: /iactalks/Talks/view/1590
CREATED:2022-05-24T17:00:00+01:00
X-WR-CALDESC: IAC Talks upcomming talks
SUMMARY:IAU G5 talk: Accelerating Computational Modeling via Neural Network
 s: Application to Exoplanet Atmospheric Retrieval/The first magnetic Heliu
 m-sdOs: which mergers are magnetic?
DESCRIPTION:IAU G5 talk: Accelerating Computational Modeling via Neural Net
 works: Application to Exoplanet Atmospheric Retrieval/The first magnetic H
 elium-sdOs: which mergers are magnetic?\nMichael Himes, Dr. Matti Dorsch\n
 \nAccelerating Computational Modeling via Neural Networks: Application to 
 Exoplanet Atmospheric Retrieval\nIIn physics and astronomy, computationall
 y expensive forward models are often an integral part of preparing experim
 ents/observations, analyzing data, and/or planning future instrumentation/
 telescopes.  In many of these cases, machine learning (ML) models, su
 ch as neural networks (NNs), can offer a significant reduction in compute 
 time with minimal loss in accuracy.  We demonstrate this approach on 
 the problem of exoplanet atmospheric retrieval, which involves on the orde
 r of 10^5 -- 10^6 radiative transfer (RT) model evaluations.  We find
  that the ML RT approach yields the same scientific conclusions as the tra
 ditional method, while requiring ~1000x less compute cost for typical setu
 ps.  We present our open-source software packages that implement this
  technique, and we discuss broader applications of this NN surrogate model
 ing approach.\n \nThe first magnetic Helium-sdOs: which mergers are m
 agnetic?\nMagnetic fields play an important role throughout stellar evolut
 ion, and among white dwarfs, the end stage of 95% of all stars, the fracti
 on of strongly magnetic systems is larger than 20%. The origins of magneti
 c white dwarfs are still under discussion, but it is likely that a signifi
 cant fraction of them are formed by stellar mergers.Several types of merge
 r remnants are thought to ignite helium fusion, such as the merger of a he
 lium-WD (He-WD) with a second He-WD, a He/C/O hybrid WD, or a low-mass mai
 n sequence star, thus forming a hot subdwarf star. The majority of hot sub
 dwarf stars are helium burning stars with very thin or no hydrogen envelop
 es. In particular, most of the hot and helium-poor He-sdO stars are though
 t to be formed by mergers. However, out of hundreds of hot subdwarfs studi
 ed over several decades, none showed detectable magnetic fields.This chang
 ed recently, when four almost identical magnetic He-sdO stars were discove
 red, with mean field strengths between 300 and 500kG.Why are these stars m
 agnetic while vast majority of other He-sdOs are non-magnetic? This questi
 on is still open. In this talk I will give a short introduction to He-sdO 
 stars and their formation and then try to highlight the differences betwee
 n the four magnetic stars and their non-magnetic cousins.
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